Dead Island is a sandbox RPG zombie apocalypse game set on the fictional island of Banoi, near Papua New Guine. Your character is one of a few people who seem immune to the infection, and can move around more freely. Thus, it falls to you to gather the people and materials needed to escape the island. Co-op gaming via steam is dynamic - you can jump in and out of other peoples games on the fly, in game. It's pretty badass.